Application of ozone based treatments of secondary effluents

Abstract

The present work was aimed at studying the efficiency of ozone in oxidation processes, coliform inactivation and Disinfection Byproducts (DBPs) formation, associated with the potential of ozone to increase the Biodegradable Dissolved Organic Carbon (BDOC) in secondary effluent with applied ozone doses of 5.0, 10.0 and 15.0 mg/L for contact times of 2, 5 and 10 min. The wastewater used in this work was collected from the Bhagwanpur Sewage Treatment Plant, Varanasi, India. Results of this experiment showed that 10 mg O₃/L O₃ for 5 min exposure was found most suitable dose for highest degradation of COD, TOC, UV₂₅₄, color, turbidity and total nitrogen parameters. The inactivation range of microbial biomass range was found in between 95% and 98%. Experiment revealed the fact that aldehydes and carboxylic acid formation were significantly related with the ozone dose and exposure time and ozone might enhance the treatment efficiency of secondary effluent treatment.

Introduction

Ozone, a highly oxidative agent, react directly or via a hydroxyl radical mechanism results into the reduction of organic content with increase of biodegradability of natural organic matter and the efficient inactivation of a wide range of microorganisms (Gottschalk et al., 2000, Takanashi et al., 2002, Xu et al., 2002, Liberti and Notarnicola, 1999). Ozonation has been used to meet discharge requirements for coliform and virus inactivation since the 1970s (Rice et al., 1981). Frequent ozonation for treatment of wastewater and drinking water is due to its ability to oxidize complex organic molecules, phenols, Endocrine Disruptive Chemicals (EDCs) and pharmaceuticals (Zwiener and Frimmel, 2000, Huber et al., 2005, Snyder et al., 2006, Kim and Tanaka, 2010). In combination of microbial disinfection make ozonation an attractive alternative for advanced wastewater treatment (Wert et al., 2007).

Generally, in the secondary treated sewage effluents, proportion of biodegradable COD which can be indicated by Biodegradable Dissolved Organic Carbon (BDOC) is relatively low. Therefore, in order to improve the treatment efficiency, a powerful oxidant which increases the BDOC of the influent is necessary. Ozone can transform some refractory organic matters to biodegradable organic ones, that is, BDOC, which can be removed easily through biodegradation process. Earlier workers reports that ozone may increase the biodegradability of organic pollutants (including natural organic matter) and induce the efficient inactivation of a wide range of microorganisms (Langlais et al., 1992, Agustina and Vareek, 2005, Wang et al., 2008, Yang et al., 2004). Microbial disinfection with the trace contaminant oxidation makes ozonation an attractive alternative for advanced wastewater treatment (Wert et al., 2007). Earlier, corona discharge was the main source for the generation of Ozone, which requires much higher resource and economy for the treatment of water with ozone. So, it was limited to certain areas viz UV lights for the drinking water treatment. Due to aforesaid reasons it was not only feasible for treatment of municipal sewage. Recent ozone generation techniques viz UV lights require lower energy consequently; costs are also reduced making the field application of Ozonation economically viable (Freire et al., 2001a, Freire et al., 2001b, Jennifer et al., 2010).

During past few decades chlorination was favored as the most common method for disinfecting wastewater effluents, because of its effectiveness, relative ease of use and low cost. However, reports indicate the fact that the chlorination of water and wastewater with organic compounds can lead to the formation of Disinfection Byproducts (DBPs) such as Trihalomethanes (THMs) (Jennifer et al., 2010) which enhances the regrowth of bacterial population, make it potentially carcinogenic and mutagenic. Also, the secondary by products are difficult to analyze and even more hazardous (Silva et al., 2010). These facts have resulted in decreased application of chlorination for disinfection on the hand ozonation, because of the several advantages over the later has been increased. Application of ozonation for wastewater treatment is more prevalent due to non production of some Disinfection Byproducts as Trihalomethans (THMs) or other chlorinated Disinfection Byproducts (DBPs) etc. (Jennifer et al., 2010).

Low molecular aliphatic organics like aldehydes, carboxylic acids are the major organic DBPs resulting from the Ozonation process. Concentration of Dissolve Organic Carbon (DOC) were greater as compare to the surface water (Buffle et al., 2006) so higher ozone dosage are required in wastewater treatment which leads more DBPs formation (Langlais et al., 1991, Melin and Odegaard, 2000, Huang et al., 2005).

Though ozonation is becoming popular for wastewater treatment, however, more studies are required to establish this method for wastewater treatment. Therefore, present study was performed with the aim to assess the extent of the removal of physico-chemical and microbial parameters as well as the formation of Disinfection Byproducts (DBPs) with different ozone dose and contact time.